1. Field of the Invention
The present invention relates to a polarizing element adapted for improvement in brightness, suppression of display blur, etc. in a liquid-crystal display device, and an optical element and a polarized light supply unit using such a polarizing element.
The present application is based on Japanese Patent Application No. Hei. 11-135333, which is incorporated herein by reference.
2. Description of the Related Art
An element constituted by a laminate of cholesteric liquid-crystal layers and a quarter-wavelength plate or an element constituted by a birefringent multilayer film is heretofore known as a polarizing element which can improve brightness of a liquid-crystal display device by overcoming such a disadvantage of the absorption type polarizing plate that about an half of incident light is absorbed as a loss (Japanese Patent Publication No. Hei. 4-268505 and PCT No. 95/17691).
The aforementioned element was designed so that linearly polarized light was made incident on an absorption type polarizing plate under coincidence of axes of polarization to hereby prevent the absorption loss. There was, however, a problem that visual recognition property was lowered largely like the case of a prism array layer because remarkable display blur occurred when a liquid-crystal display device using the aforementioned element was viewed obliquely. Incidentally, in the prism array layer for achieving improvement of brightness by light path control, visual recognition property was lowered greatly at an obliquely viewing angle not smaller than about 40 degrees because of lowering of brightness.
An object of the present invention is to develop a polarizing element, an optical element and a polarized light supply unit, which can generate polarized light low in absorption loss due to an absorption type polarizing plate, which can supply incident light to liquid-crystal cells with good light utilizing efficiency and which can form a liquid-crystal display device excellent in brightness and little in display blur.
According to an aspect of the present invention, there is provided a polarizing element having a function of separating natural light into reflected or transmitted light composed of polarized light, wherein a half-reflecting wavelength in each position in a surface of the polarizing element ranges within xc2x110 nm relative to a half-reflecting average wavelength. Hereupon, the half-reflecting wavelength is a wavelength which is located at a long or short wave side of a wavelength exhibiting maximum reflectivity on the basis of a spectrum of reflected light in a predetermined wave range in which the natural light is separated into the reflected light and the transmitted light. And the half-reflecting wavelength exhibits reflectivity of 50% with respect to the maximum reflectivity. The half-reflecting average wavelength is an average of half-reflecting wavelengths in the whole surface of the polarizing element.
The present invention further provides: an optical element including the aforementioned polarizing element, and an absorption type polarizing plate laminated on the polarizing element through an adhesive layer; a polarized light supply unit including a surface light source provided with a reflection layer, and the aforementioned polarizing element or optical element disposed above the surface light source; and a liquid-crystal display device including the polarized light supply unit, and liquid-crystal cells disposed on the light output side of the polarized light supply unit through an absorption type polarizing plate.
According to the present invention, there can be formed a liquid-crystal display device which is so excellent in a polarized light separating function that polarized light low in absorption loss due to an absorption type polarizing plate is provided with good incident light utilizing efficiency and which is so excellent in brightness so that display blur such as coloring is suppressed even at an obliquely viewing direction. This is based on suppression of scattering in half-reflecting wavelength in respective positions in a surface relative to a half-reflecting average wavelength.
Features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.